Battery systems are widespread and provide energy storage to power a wide range of devices, electric vehicles, and energy storage for use as backup power systems during electrical grid failures or as energy storage systems that store excess power from wind, solar, and other electrical power generation systems for later use. Monitoring various characteristics of the battery while the battery operates is important to ensuring that the battery can provide electrical energy as needed for various applications and to ensure that the battery is not damaged or unduly degraded during operation.
One challenge that occurs in monitoring batteries is that some types of battery measurements can only be performed with great accuracy when the battery is disconnected from an electrical load to enable the battery to reach a quiescent state. For example, one well-known parameter of a battery that changes over time as the battery charges and discharges is known as the open cell voltage (OCV). As used herein, the term “open cell voltage” refers to the voltage level that is measured across an anode terminal and a cathode terminal of the battery when the battery is disconnected from any load for a sufficient time to return to a quiescent state, where the sufficient time is typically on the order of several seconds to several minutes depending upon the battery configuration. When the battery is in the quiescent state, the OCV can of course be measured directly using a simple voltmeter as is known to the art.
However, the OCV cannot be measured using a direct voltage measurement when the battery is connected to a load during operation in which the battery produces a substantial amount of current to drive a load. The OCV of the battery, which changes as the battery charges and discharges during operation, is one characteristic that is used to determine the state of charge (SoC) and state of health (SoH) of a battery during operation of the battery. The state of charge (SoC) is defined as the ratio between the residual charge and the total available charge and state of health (SoH) is defined as the available capacity of the battery between two specified voltage limits. If the OCV of the battery cannot be determined accurately, then the inaccurate OCV value can reduce the accuracy of estimating the state of charge and state of health in the battery. To name just one negative impact of inaccurate battery characteristic determination in a practical setting, an electric vehicle may be unable to produce an accurate estimate of a remaining driving range during operation if any of the OCV, SoC, and SoH of the battery cannot be determined accurately. Consequently, improvements to methods for estimating the OCV and other battery characteristics that are related to the OCV while a battery remains connected to a load would be beneficial.